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Biophys. J. BioFAST: First Published May 19, 2006. doi:10.1529/biophysj.105.078501
© 2006 by the Biophysical Society.

A more recent version of this article appeared on August 1, 2006.
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PHOTOBIOPHYSICS

A spatial model of the chromatophore vesicles of Rhodobacter sphaeroides and the position of the cytochrome bc1 complex

Tihamer Geyer 1* and Volkhard Helms 1

1 Saarland University

* To whom correspondence should be addressed. E-mail: tihamer.geyer{at}bioinformatik.uni-saarland.de.

Submitted on November 29, 2005
Revised on January 9, 2006
Accepted on 26 April 2006


  Abstract
The photosynthetic apparatus of purple bacteria is generally considered a well studied and understood system. However, recent AFM images of flattened chromatophore vesicles from Rb. sphaeroides restarted a debate about the stoichiometry and positions of the membrane proteins, with the interpretations of the observed images only partly being in agreement with earlier models. The most puzzling observation from the recent images is that the cytochrome bc1 complex, which is a central part of the photosynthetic apparatus, seems to be missing on the chromatophore vesicles, even when these were extracted from photosynthetically grown bacteria. From the available information on the geometry of the vesicle and of the proteins we reconstructed here a three--dimensional model vesicle at molecular resolution. Its central feature, also determining its diameter of about 45 nm, is an equatorial array of LH1 dimers, lined by a region of LH2 rings. This naturally puts the cytochrome bc1 complexes and the ATPase at the vesicle's poles. This spatial model may explain why the vesicle's endcaps with the bc1 complexes are lost during the preparatory steps of the imaging process together with the ATPase and are therefore absent from the available images.

Key Words: PufX, Rhodobacter sphaeroides, chromatophore vesicle, cytochrome bc1 complex




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Copyright © 2006 by the Biophysical Society.